1. Field of the Invention
The present invention relates to a cradle for a portable content playback apparatus, and an amplifying device to which the cradle is connected.
2. Description of the Related Art
A personal computer (PC) or a portable content playback apparatuses (hereinafter referred to as a digital audio player (DAP)) is typically provided with a recording medium such as an HDD, and capable of recording audio files in the HDD and playing the audio files recorded in the HDD. (1) When playing an audio file recorded in the PC and listening to an audio content, the PC is connected to an amplifying device by a user operation. The PC decodes the audio file and transmits audio data to the amplifying device, and sound and voice are played by the amplifying device. (2) When transferring an audio file recorded in the PC to the DAP and recording the file in the DAP, the PC and the DAP are connected via an USB cable by a user operation. The PC transfers the audio file recorded in the HDD to the DAP, and the DAP records the transferred audio file in the HDD. (3) When playing an audio file recorded in the DAP and listening to an audio content, the DAP is connected to a cradle, and the cradle is connected to amplifying device by a user operation (see Japanese Patent publication NO. 2006-244607, for example). The DAP decodes the audio file and transmits audio data to the amplifying device via the cradle, and sound and voice are played by the amplifying device. In order to carry out the operations (1) to (3) described above, the PC, the DAP, the cradle, and the amplifying device are required to be connected and disconnected every time by the user operation, which is extremely cumbersome.
On the other hand, the DAP can be connected to the PC or the cradle via the USB, and a battery of the DAP is charged by the PC or the cradle supplying a voltage for electrical charge. Some DAPS are such that the battery of the DAP is charged by the voltage for electrical charge when a charging command is supplied from a host controller via datalines D+ and D− of the USB at a predetermined time interval, and not charged when the charging command is not supplied from the host controller at a predetermined time interval. Accordingly, a problem has been noted that, when the PC is turned off, even though the voltage for electrical charge is supplied from the PC to the DAP, the charging command is not supplied from the PC to the DAP and thus the battery of the DAP cannot be charged.